Low power consumption is increasingly important in electronic systems. It is desirable to keep many blocks of the electronic system in sleep mode, where active power is very low, as long and as often as possible. Typical methods in doing so are to wake up blocks, such as the processor or radio, on a set interval determined by a clock or timer. Another well-known method is to wake up blocks when the signal to be processed exceeds a certain voltage threshold. These methods, however, cannot wake up the electronic blocks very selectively due to its simplicity or due to it being restricted by a predetermined time interval.